use warnings;
use strict;

while (<DATA>) {
    if (/ ^ (\d+) [.] (\d+) [.] (\d+) $ /x) {
        print "$1 $2 $3\n";
    }
}

__DATA__
7.55.3
12.0.2

##</code><code>##

7 55 3
12 0 2

##</code><code>##

    if (/ ^ (\d{1,2}) [.] (\d{1,2}) [.] (\d{1,2}) $ /x) {